RELIABILITY OF NAVIGATION MEASUREMENTS OF THE BIEPICONDYLAR AXIS FOR KNEE PROSTHESES: CORRELATIONS WITH THE PREOPERATIVE SCAN

Abstract

Purpose of the study: The purpose of rotating the femoral piece, using an indepenent cut strategy, is to «correct» for epiphyseal torsion of the distal femur and thus obtain a biepicondylar axis parallel to the posterior bicondylar axis. It is known however that epiphyseal torsion of the distal femur is highly variable from one individual to another. Intraoperative identification of the biepicondylar line enables appropriate rotation, as long as the data collected are reliable. The purpose of this study was to determine the reliability of intraoperative biepicondylar axis measurements made with navigation systems and to compare the results with the preoperative scan taken as the gold standard.

Material and methods: This prospective study included 60 degenerative knees undergoing total knee arthroplasty. The angle of epiphyesael rotation of the distal femur was measured on the preoperative computed tomography scan and intraoperatively with the navigation system which identified the biepicondylar line and the posterior bicondylar line. Statistical regression lines were determined.

Results: The rotation measured on the preoperative scan was 7.1±2.4° and by the intraoperative navigation system 3.2±4.3°. There was a very weak statistical correlation between the preoperative measurement and the intraoperative navigation measurement (p=0.234, R =0.320).

Discussion: Intraoperative identification of the biepicondylar axis is not reliable. Navigation does not enable an accurate assessment of the distal epiphyseal torsion of the femur and thus the proper rotation to give to the femoral piece. The only reliable measurement of the epiphyseal rotation of the distal femur is made on the preoperative computed tomography.